managing-scylladb

name	managing-scylladb
description	Use when working with Scylladb — scyllaDB cluster management, shard-per-core analysis, compaction strategy tuning, and CQL performance diagnostics. Covers node health, tablet distribution, workload prioritization, repair scheduling, and latency histogram analysis. Read this skill before any ScyllaDB operations.
connection_type	scylladb
preload	false

ScyllaDB Management Skill

Monitor, analyze, and optimize ScyllaDB clusters safely.

MANDATORY: Discovery-First Pattern

Always check cluster status and list keyspaces before any CQL operations. Never assume keyspace or table names.

Phase 1: Discovery

#!/bin/bash

SCYLLA_HOST="${SCYLLADB_HOST:-localhost}"
SCYLLA_PORT="${SCYLLADB_PORT:-9042}"

echo "=== Cluster Status ==="
nodetool -h "$SCYLLA_HOST" status

echo ""
echo "=== Scylla Version ==="
nodetool -h "$SCYLLA_HOST" version

echo ""
echo "=== Keyspaces ==="
cqlsh "$SCYLLA_HOST" "$SCYLLA_PORT" -e "DESCRIBE KEYSPACES;"

echo ""
echo "=== Cluster Description ==="
nodetool -h "$SCYLLA_HOST" describecluster

echo ""
echo "=== Shard Info ==="
curl -s "http://$SCYLLA_HOST:10000/system/uptime_ms" 2>/dev/null
curl -s "http://$SCYLLA_HOST:10000/storage_service/hostid/local" 2>/dev/null

Phase 1 outputs: Node states, Scylla version, keyspace list, cluster topology, shard count.

Phase 2: Analysis

#!/bin/bash

SCYLLA_HOST="${SCYLLADB_HOST:-localhost}"
KEYSPACE="${1:-my_keyspace}"

echo "=== Keyspace Details ==="
cqlsh "$SCYLLA_HOST" -e "DESCRIBE KEYSPACE $KEYSPACE;"

echo ""
echo "=== Table Stats ==="
nodetool -h "$SCYLLA_HOST" tablestats "$KEYSPACE" | grep -E "Table:|Space used|Number of|Compaction|Read Latency|Write Latency" | head -30

echo ""
echo "=== Compaction Stats ==="
nodetool -h "$SCYLLA_HOST" compactionstats

echo ""
echo "=== Scheduling Groups (Workload Prioritization) ==="
curl -s "http://$SCYLLA_HOST:10000/task_manager/list_module_tasks/compaction" 2>/dev/null | head -10

echo ""
echo "=== Repair Status ==="
nodetool -h "$SCYLLA_HOST" repair_status 2>/dev/null || \
    nodetool -h "$SCYLLA_HOST" netstats | grep -A5 "Repair"

echo ""
echo "=== Thread Pool Stats ==="
nodetool -h "$SCYLLA_HOST" tpstats |  -25

Output Format

SCYLLADB ANALYSIS
=================
Cluster: [name] | Nodes: [count] | Version: [version]
Keyspaces: [count] | Shards/Node: [count]

ISSUES FOUND:
- [issue with affected keyspace/node]

RECOMMENDATIONS:
- [actionable recommendation]

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative